From the Rolls-Royce experimental archive: a quarter of a million communications from Rolls-Royce, 1906 to 1960's. Documents from the Sir Henry Royce Memorial Foundation (SHRMF).
Road wheel diameter, booming, roughness, and exhaust manifold tests, including a sketch of a manifold design.
| Identifier | WestWitteringFiles\T\March1929-December1929\ Scan026 | |
| Date | 12th March 1929 guessed | |
| (4) ROAD WHEEL DIAMETER. A final run was made with the Sch. (b) SS.{S. Smith} changing the 33" road wheels for 32" on the spot so that the minimum delay occurred between tests. It was difficult to believe that this small change would make any difference, especially as it was almost necessary to read the tyre numbers to know which were the smaller wheels, but the results obtained with the latter were appreciably inferior on the test road. BOOMING AND ROUGHNESS. It was very difficult in the earlier stages of this development to determine the main cause of the booming noise which was rather pronounced on some of the SS.{S. Smith} cars, and to avoid being obsessed with the phenomenon it was necessary to refer back at intervals to accepted standards such as London trials cars and 14-EX. to readjust the sense of proportion. Briefly the engine roughness as would be expected disappeared as the engine mounting was made more flexible. The booming noise manifested itself apparently from under the bonnet the moment the throttle was opened, and did not occur on the over-run. It did not appear to be directly associated with the nature of the engine mounting, but more with the torsional rigidity of the frame, and it was unaffected by changes in the exhaust manifold. The booming became less as the chassis was improved from the point of view of not wobbling on the road, and the examples of both schemes (a) and (b) are a very considerable improvement, and (b) is possibly quite free from this trouble. EXHAUST MANIFOLDS & SILENCER. The question of the silence of the exhaust remains to be determined once the policy with regard to frame and engine mounting is settled. Regarding the manifold we made one up from welded steel with an expansion box on the lines of the old Silver Ghost, as in sketch, but although this was thought once to effect a slight improvement it did not alter the booming noise which recurred when the throttle was opened. There are 3 manifolds available for experiment - the original type in thicker larger Staybrite tube LeC. 2657. the one above, & the cast iron LeC. 2638. | ||